Germanium(IV) adsorption from aqueous solution using a kelex-100 functional adsorbent

The removal of germanium from acid solution systems using a Kelex-100 [7-(4-ethyl-1-methyloctyl)-8- hydroxyquinoline] functional sol-gel adsorbent was investigated. Kelex-100 has been used for separating metals such as Ga(III), Co(II), Cd(II), Pb(II), and Cu(II) from aqueous solution by solvent extraction and liquid membranes. The goal of this work was to demonstrate that elutable mesoporous organo-ceramic adsorbents based on Kelex-100 can be synthesized for the selective separation of germanium from simulated leachate solution. The speciation diagram of Ge(IV) in an aqueous system with varying pH was prepared and evaluated by analysis of the equilibrium equations. The Langmuir adsorption isotherm was found to provide a satisfactory fit of the adsorption data, and the uptake capacity at pH 6.0 was found to be 0.33 mmol/g (23 mg/g). A kinetics study conducted on a germanium(IV) solution in a batch reactor at different pH values showed a high rate of adsorption relative to other adsorbents [Inukai et al. Anal. Sci. 2001, 1, 1117-1120; Marco et al. Carbon 2007, 45 (13), 2519-2528; Pokrovsky et al. Geochim. Cosmochim. Acta 2006, 70, 3325-3341]. The adsorbent exhibited a high selectivity toward Ge(IV) and negligible adsorption of As(II), Sb(II), Ni(II), and Zn(II). Adsorption tests in a fixed-bed column showed a sharp breakthrough curve. Stripping of the germanium-loaded column bed was achieved using 1 M HCl. Eleven cycles of the adsorption and desorption process were performed with this Kelex-100 functional adsorbent, named SOL-KELEX. The adsorbent maintained 70% of its original capacity through six cycles and lost 50% of its capacity through 11 cycles of operation. The Kelex-100 functional adsorbent was found to be an effective sorbent material for the separation of germanium(IV) from aqueous solutions.